A rhodamine based “off–on” fluorescent sensing probe for selective detection of Fe3+ in both aqueous media and a cell environment has been developed.

A colorimetric and ratiometric fluorescent hydrazine reactive probe COUMA2 has been developed. In aqueous solution, hydrazinolysis of COUMA2 results in deacetylation affording fluorescent products displaying dual emissive peaks at 500 and 655 nm. 50 μM NH2NH2 can induce a ratiometric change of fluorescent signal from COUMA2 by a factor of 4.89.

A coumarin-based fluorescent chemosensor CAQA has been synthesized. It can selectively and sensitively recognize Cu2+ in aqueous acetonitrile solutions. Using the Cu-containing complex CAQA–Cu2+ as a sensing ensemble, the device demonstrates highly selective recognition of His/biothiols and was applied in fluorescence imaging of histidine in hard-to-transfect living cells.

A ratiometric fluorescent Zn2+ chemosensor, SPQH, based on spirobenzopyran platform, was synthesized. In aqueous HEPES 7.4 buffer solution, upon chelation with Zn(II), SPQH demonstrates high selectivity and subnanomolar sensitivity for zinc ion with 36-fold enhancement in the NIR fluorescence output.

A ratiometric fluorescence sensing ensemble, Cd2+–ACAQ, was developed and exploited for the selective detection of polyphasphates in 8:2 buffed HEPES/MeOH solutions.A ratiometric fluorescent sensing ensemble, Cd2+–ACAQ, was developed and exploited for the detection of polyphosphates in 8:2 buffered HEPES/MeOH solutions.

In recent decades, numerous spiropyran derivatives have been designed and utilized for optical sensing of metal ions. However, there is still less research on spiropyran-based anion sensors. In this work, a new spiropyran compound (L) appended with a pendant bis(2-pyridylmethyl)amine was synthesized and used in fluorescent sensing of pyrophosphate ion (PPi) in aqueous solution. The molecular recognition and signal transduction are based on the cooperative ligation interactions and the ligation-induced structural conversion of the spiropyran, which leads to a significant change in the photophysical property of the spiropyran. In an ethanol/water solution (30:70, v/v) at pH 7.4, ligation of L with Zn2+ causes an intense fluorescence emission at 620 nm at the expense of the original fluorescence at 560 nm. Once PPi was introduced, interaction between PPi and the L−Zn2+ complex leads to full quenching of the 620 nm band emission which was concomitant with recovery of the 560 nm band emission, and the fluorescence intensity ratio, F560/F620, is proportional to the PPi concentration. Under the optimum condition, the L−Zn2+ complex responds to PPi over a dynamic range of 1.0 × 10−6 to 5.0 × 10−4 M, with a detection limit of 4.0 × 10−7 M. The fluorescence response is highly selective for PPi over other biologically related substrates, especially the structurally similar anions, such as phosphate and adenosine triphosphate. The mechanism of interaction among L, Zn2+, and PPi was primarily studied by 1H NMR, 31P NMR, and HRMS. To demonstrate the analytical application of this approach, the PPi concentration in human urine was determined. It was on the order of 3.18 × 10−5 M, and the mean value for urinary PPi excretion by three healthy subjects was 62.4 μmol/24 h.

By conjugating spiropyran chloride 8 with 2-amino-N-(quinolin-8-yl)acetamide (5), multifunctionalized spirobenzopyran derivative SPQN was designed and synthesized as a water soluble colorimetric and fluorescent turn-on chemosensor for Zn2+. In 50% aqueous ethanol buffer solution, SPQN displayed a selective chelation fluorescence enhancement (16-fold) at 650 nm and visible color change (from colorless to red) with Zn2+ among the metal ions examined. In addition, as the third channel to display the metal binding characteristics of SPQN, operating on an efficient FRET process between the quinoline and the merocyanine moiety of the sensor, ratiometric determination of Zn2+ can be realized.

A novel FRET fluorescent sensor SPAQ containing 8-aminoquinoline (donor) and spiropyran derivative (acceptor) was designed and synthesized for detecting Zn2+. The probe successfully exhibited a fluorescence turn on and ratiometric response for Zn2+ in ethanol solution with high selectivity. Upon excitation at 370 nm, the modulation of the emission intensity of SPAQ at 645 and 470 nm was achieved in the presence of Zn2+ by fluorescent resonance energy transfer (FRET) and chelation-enhanced fluorescence (CHEF) effects.A FRET fluorescent chemosensor SPAQ was designed and synthesized for ratiometric detection of Zn2+ with high selectivity and sensitivity.

We describe a new nuclear staining strategy by in vivo anchoring Hoechst 33342, a commonly used nuclear staining organic dye, onto water-soluble N-acetylcysteine (NAC)-capped CdTe quantum dots (QDs). The strong H-bonding and electrostatic interaction between the organic dye and the QDs entice the positively charged nuclear staining agent in carrying effectively the bright QDs into the nucleus of living cells. Dynamic confocal imaging studies indicated that all visible light emitting NAC-capped QDs with emitting wavelength ranging from 530 to 602 nm can be successfully targeted to the nucleus of the living cells within 30 min. The minimum quantity of Hoechst 33342 as the anchoring agent required in carrying QDs to the nucleus is found to be 5 μg/mL. In essence, a simple, fast, and specific bioimaging of the nucleus in living cells by QDs is accomplished.

We have developed a new fluorescent ensemble probe comprising an ionic conjugate between water-soluble thioglycolic acid (TGA) capped CdTe quantum dots (QDs) and Ru(bpy)2(dppx)2+ for the dual-color detection of complementary double-stranded DNAs (dsDNA). To provide the platform for DNA detection, the Ru-complex was first employed as an effective fluorescence quencher to TGA capped QDs via photoinduced electron transfer process. Because of its strong binding affinity with Ru(bpy)2(dppx)2+, complementary dsDNA can break up the low fluoresced ionic ensemble, set free the luminescent QDs, and concomitantly generate the Ru(bpy)2(dppx)2+ intercalated DNA complex. Thus, the recognition of dsDNA by Ru(bpy)2(dppx)2+ can be realized via both the restoration of QDs fluorescence and the emergence of a new fluorescence emission signal of the quencher−substrate at 609 nm, while single-stranded DNA, ribonucleic acid, bovine albumin serum, and biological relevant metal ions cannot produce the similar results. Therefore, a simple, fast, sensitive, and highly selective assay for dsDNA has been realized.

Spiropyrans are an attractive starting point in design of optical approaches for metal ions sensing. However, the high background in aqueous solution and non-specific chelation of the spiropyran with heavy metal ions has hindered their application as reliable sensors for environmental and biological species. Here, we report on a new spiropyran-based approach for sensitive and selective sensing of Hg2+ in aqueous solution, based on cooperative ligation interactions among the spiropyran probe, an intermediate, cysteine, and the metal ion. To test the feasibility of this design, three spiropyran scaffolds, L1–L3, with different ligation functions at the 8′-position were examined as model systems. The results demonstrate that by using cysteine, a potential ligand of Hg2+, the spiropyran could detect 1.0 × 10−7 M Hg2+ in aqueous solution. Due to the specific metal–amino acid interaction, the approach exhibits selective response toward Hg2+ over other metal ions and anions, although possible interference from Cu2+ has to be considered at the high level of the metal ion. This approach has been used for the determination of Hg2+ in water samples containing potential interferents with satisfactory recovery.

The synthesis of water-soluble near-infrared (NIR)-emitting quantum dots (QDs) in aqueous solution has received much attention recently. However, the stabilizer 3-mercaptopropionic acid, commonly used in the synthesis of NIR-emitting QDs, is notorious for its toxicity and awful odor. Here we chose thiol ligand N-acetyl-l-cysteine (NAC) as the ideal stabilizer and have successfully employed it to synthesize high-quality NIR-emitting CdTe/CdS QDs in a one-step process via a simple hydrothermal route. NAC possesses favorable properties such as nontoxic, nonvolatile, inexpensive, and good water-solubility. Our as-prepared NIR-emitting CdTe/CdS QDs exhibit high photoluminescence quantum yields (45−62%), narrow full-width at half-maximum, and high photostability, thanks to the formation of a protective CdS shell on the CdTe core through the decomposition of NAC in the hydrothermal route under high temperature. The prepared QDs can be applied for bioimaging due to its excellent water-solubility and biological compatibility. The core/shell structure of the NIR-emitting CdTe/CdS QDs was verified by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, selected area electron diffraction, and X-ray powder diffraction. The formation mechanism of these QDs is discussed in detail.

The ditopic fluorescent photoinduced electron transfer (PET) amino acid sensory probes 1a and 1c were designed and synthesized from cholic acid. To confer the probes with specific binding ability, an amidothiourea moiety and a cyclic diamino-chiral receptive site were introduced on the C17 side chain and the C7 and C12 hydroxyl pendants, respectively. In acetonitrile, the probes demonstrated differential binding toward trifunctional amino acids like serine, lysine, threonine and tyrosine against other simple amino acids. Enantioselectivities (KD/KL) of up to 8.9 and sensitivities in the micromolar range with the probes were observed for trifunctional amino acids.

A novel ditopic cholic acid-based fluorescent chemosensor for ATP, 1a, was designed and synthesized. Its interactions with phosphates, AMP, ADP, ATP, CTP, GTP, and TTP have been investigated. When ATP was added to a 1 : 1 aqueous CH3CN solution of the sensor at pH 7.4, a significant decrease in fluorescence of 1a was observed, whereas other guest molecules showed a much smaller effect. The complex between 1a and ATP was confirmed through combined UV, 1H, 13C and 31P NMR spectroscopic methods. The uniqueness of the new sensor is that it binds with ATP 33–124 times more selectively than other nucleotides, as evidenced from the respective binding constants. 1a is a highly sensitive sensing probe; as little as 30 nM ATP can cause 15% fluorescence quenching of the sensor.

A number of bicyclic chiral sultams were synthesized based on 1,3-dipolar cycloaddition reactions of nitrile oxides and nitrones with prop-1-ene-1,3-sultone. The corresponding N-enoyl sultams were prepared by acylation. Their relative effectiveness as new chiral auxiliaries in asymmetric synthesis was evaluated for the asymmetric Diels–Alder reactions with cyclopentadiene. Good chemical yield and excellent endo selectivity were observed. The relationship between the structure and their effectiveness in promoting asymmetric induction of the synthetic chiral sultams was investigated.(3aR,6aR)-3-Phenyl-5-(S)-α-phenylethyl-4,5-thiazolidine-4,4-dioxide[3,4-d]-2-isoxazolineC18H18N2O3S[α]D21=+126.2 (c 0.9, CHCl3)Source of chirality:asymmetric synthesisAbsolute configuration:(3aR,6aR)(3R,3aR,6aR)-2-Benzyl-3-phenyl-5-(S)-α-phenylethyl-4,5-thiazoline-4,4-dioxide[3,4-d]isoxazolidineC25H26N2O3S[α]D21=-32.2 (c 108, CHCl3)Source of chirality:asymmetric synthesisAbsolute configuration:(3R,3aR,6aR)(3aR,6aR)-3-Phenyl-4,5-thiazolidine-4,4-dioxide[3,4-d]-2-isoxazolineC10H10N2O3S[α]D21=-141.5 (c 0.43, CHCl3)Source of chirality:asymmetric synthesisAbsolute configuration:(3aR,6aR)(3R,3aR,6aR)-2-Benzyl-3-phenyl-4,5-thiazoline-4,4-dioxide[3,4-d]isoxazolidineC17H18N2O3S[α]D21=-55.3 (c 1.25, CHCl3)Source of chirality:asymmetric synthesisAbsolute configuration:(3R,3aR,6aR)(3aR,6aR)-3-Phenyl-5-trans-crotonyl-4,5-thiazoline-4,4-dioxide[3,4-d]-2-isoxazolineC14H14N2O4S[α]D21=+151.8 (c 0.90, CHCl3)Source of chirality:asymmetric synthesisAbsolute configuration:(3aR,6aR)(3R,3aR,6aR)-2-Benzyl-3-phenyl-5-trans-crotonyl-4,5-thiazoline-4,4-dioxide[3,4-d]isoxazolidineC21H22N2O4S[α]D21=-14.9 (c 1.67, CHCl3)Source of chirality:asymmetric synthesisAbsolute configuration:(3R,3aR,6aR)(3aR,6aR)-5-N-{(1R*,2S*,3R*,4S*)-3-Methyl-bicyclo[2,2,1]hept-5-en-2-formyl}-3-phenyl-4,5-thiazolidine-4,4-dioxide[3,4-d]-2-isoxazolineC19H20N2O4S[α]D18=+294 (c 0.81, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (3aR,6aR)-5-N-(1R*,2S*,3R*,4S*)(3aS,6aS)-5-N-{(1S*,2R*,4R*)-Bicyclo[2,2,1]hept-5-en-2-formyl}-3-phenyl-4,5-thiazolidine-4,4-dioxide[3,4-d]-2-isoxazolineC18H18N2O4S[α]D18=-239.2 (c 0.80, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (3aS,6aS)-5-N-(1S*,2R*,4R*)(3R,3aR,6aR)-5-N-{(1R*,2S*,3R*,4S*)-3-Methyl-bicyclo-[2,2,1]hept-5-en-2-formyl}-3-phenyl-4,5-thiazolidine-4,4-dioxide[3,4-d]isoxazolidineC20H28N2O4S[α]D18=+42.2 (c 1.05, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (3R,3aR,6aR)-5-N-(1R*,2S*,3R*,4S*)(3R,3aR,6aR)-5-N-{(1R*,2S*,3R*,4S*)-3-Methyl-bicyclo[2,2,1]-hept-5-en-2-formyl}-3-pyrenyl-4,5-thiazolidine-4,4-dioxide[3,4-d]isoxazolidineC36H32N2O4S[α]D21=+83.3 (c 1.70, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (3R,3aR,6aR)-5-N-(1R*,2S*,3R*,4S*)

A new proton-selective fluorescing indicator, 3,3′,5,5′-tetramethyl-N-(9-anthrylmethyl)benzidine (TMANB) has been synthesized and applied in an optode membrane for the determination of lead ion that works on the basis of a cation-exchange mechanism. When embedded in a plasticized poly(vinyl chloride) (PVC) membrane containing lead ionophore (tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide)) and a lipophilic anionic site [potassium tetrakis(4-chlorophenyl)borate], TMANB shows a significant fluorescence signal change on exposure to aqueous HCl solution containing lead ion, which exhibits the theoretically expected fluorescence response to lead ion concentration. The selectivity, response time, reproducibility and reversibility, and lifetime of the optode membrane were discussed.

A fast responsive sodium ion selective fluorescent optode membrane mounted on an optical fiber has been developed. The sensing membrane contained fluorescein octadecyl ether octadecyl ester (FODEE), potassium tetrakis(4-chlorophenyl) borate (KTpClPB) and a calix[4]arene tetraester in a plasticized poly(vinyl chloride) (PVC) matrix. It exhibited a reversible response to Na+ in 0.5 mol/l of HCl in the concentration range of 1.0×10−6 to 0.1 mol/l. The selectivity, response time, reproducibility and lifetime of the optode membrane were discussed. The practical use of this sensor was demonstrated by real sample analysis in complex sample solutions such as beverage and urine samples.

Formaldehyde was sampled with the use of a standard miniature glass fibre filter coated with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH). The formaldehyde hydrazone formed [i.e., the adduct of formaldehyde (HCHO) and MBTH] was desorbed from the filter with water and then oxidised by an iron(III) chloride–sulfamic acid solution to form a blue cationic dye in acidic medium which was subsequently determined by visible absorption at 628 nm. The recovery of HCHO as the cationic dye from MBTH-coated filters is 87–102% in the range 0.065–2.9 μg of HCHO. This corresponds to 4.3–193.3 μg m−3 in a 15 L air sample. The collection efficiency of the MBTH-coated filter is higher than 90%. When the filter sampling system is used in active mode, air can be sampled at a rate of up to 1 L min−1, affording an overall sensitivity of about 3 μg m−3, corresponding to about 2 ppb v/v HCHO at 1 atm and 273 K. The method was successfully applied to the determination of HCHO in samples of indoor and outdoor air with satisfactory results.

Enantiomerically pure sultams (+)-4 and (−)-4 were synthesized from tricyclic sultone 1via a four-step reaction sequence. Their uses as new chiral auxiliaries in asymmetric Diels-Alder reactions with diastereoselectivity up to 94:6 are presented.Graphic

A coumarin-based fluorescent chemosensor CAQA has been synthesized. It can selectively and sensitively recognize Cu2+ in aqueous acetonitrile solutions. Using the Cu-containing complex CAQA–Cu2+ as a sensing ensemble, the device demonstrates highly selective recognition of His/biothiols and was applied in fluorescence imaging of histidine in hard-to-transfect living cells.

By conjugating spiropyran chloride 8 with 2-amino-N-(quinolin-8-yl)acetamide (5), multifunctionalized spirobenzopyran derivative SPQN was designed and synthesized as a water soluble colorimetric and fluorescent turn-on chemosensor for Zn2+. In 50% aqueous ethanol buffer solution, SPQN displayed a selective chelation fluorescence enhancement (16-fold) at 650 nm and visible color change (from colorless to red) with Zn2+ among the metal ions examined. In addition, as the third channel to display the metal binding characteristics of SPQN, operating on an efficient FRET process between the quinoline and the merocyanine moiety of the sensor, ratiometric determination of Zn2+ can be realized.

The ditopic fluorescent photoinduced electron transfer (PET) amino acid sensory probes 1a and 1c were designed and synthesized from cholic acid. To confer the probes with specific binding ability, an amidothiourea moiety and a cyclic diamino-chiral receptive site were introduced on the C17 side chain and the C7 and C12 hydroxyl pendants, respectively. In acetonitrile, the probes demonstrated differential binding toward trifunctional amino acids like serine, lysine, threonine and tyrosine against other simple amino acids. Enantioselectivities (KD/KL) of up to 8.9 and sensitivities in the micromolar range with the probes were observed for trifunctional amino acids.

A novel ditopic cholic acid-based fluorescent chemosensor for ATP, 1a, was designed and synthesized. Its interactions with phosphates, AMP, ADP, ATP, CTP, GTP, and TTP have been investigated. When ATP was added to a 1 : 1 aqueous CH3CN solution of the sensor at pH 7.4, a significant decrease in fluorescence of 1a was observed, whereas other guest molecules showed a much smaller effect. The complex between 1a and ATP was confirmed through combined UV, 1H, 13C and 31P NMR spectroscopic methods. The uniqueness of the new sensor is that it binds with ATP 33–124 times more selectively than other nucleotides, as evidenced from the respective binding constants. 1a is a highly sensitive sensing probe; as little as 30 nM ATP can cause 15% fluorescence quenching of the sensor.